Polymer/polyol compositions suitable for use in producing polyurethane foams are known materials. Such compositions can be produced by polymerizing one or more olefinically unsaturated monomers dissolved or dispersed in a polyol in the presence of a free radical catalyst. These polymer/polyol compositions have the valuable properties of imparting to polyurethane foams produced therefrom higher load-bearing properties than are imparted by unmodified polyols and of imparting higher modulus to solid polyurethane elastomers made therefrom than are imparted by unmodified polyols.
The polymer/polyol compositions that have found commercial acceptance prior to the present invention are primarily compositions produced from polyols and acrylonitrile or acrylonitrile-styrene mixtures. Such compositions usually contain about 80 wt.% polyol and about 20 wt.% polymer. The polymer is an acrylonitrile homopolymer or copolymers of approximately 40 to 55 wt.% acrylonitrile and 60 to 45 wt.% styrene. Some of the polymer is grafted to the polyol to form a graft copolymer which stabilizes the remaining polymer particles so they remain dispersed in the polyol. The higher load-bearing properties and higher modulus of polyurethanes produced from such polymer/polyol compositions is attributed to the polymer in the compositions.
Attempts to produce, on a commercial scale, polymer/polyol compositions that have much more than 20 wt.% polymer and that, consequently, impart even higher load-bearing properties and modulus to polyurethanes involve various difficulties. Thus, when the polymer in the composition is made from acrylonitrile alone and the polymer content is much above 20 wt.%, the compositions usually have undesirably high viscosities and large granules usually form. Such granules create difficulties in the preparation, handling and utilization of the compositions (e.g., the granules can clog the reactors in which the compositions are made and the filters in the feed lines in the relatively sophisticated machines in which polyurethane foams are now produced from the compositions). Similarly, when the polymer in the composition is made from acrylonitrile and styrene in the relative amounts indicated above and the polymer content is much above 20 wt.%, excessive amounts of large granules are usually formed.
The difficulties in producing polymer polyol compositions wherein the polymer is made from acrylonitrile and styrene are particularly severe in the process of the runs of Example 6 of Canadian Patent 785,835 wherein such monomers were employed. The latter process entails the production of very unsatisfactory compositions due to granule formation. A considerable improvement in the particulate nature of such polymer polyol compositions is achieved when the process described in Belgian Patent 788,115 is employed. However, even the process of the latter patent leaves room for further improvement in terms of granule formation at polymer contents much above 20 wt.-%.
Prior commercial polymer/polyol compositions have been made from polyols having molecular weights of about 3000 and higher. The use of lower molecular weight polyols provides polymer/polyol compositions convertible to polyurethanes having properties that can be conveniently achieved only by having low molecular weight polyol moieties in the polyurethane structure. However, the use of lower molecular weight polyols has not proven completely satisfactory because the resulting polymer/polyol compositions are not as stable to phase separation as is desirable by present industrial standards, especially at polymer contents of 15 wt.% and higher.
The viscosity of a polymer/polyol composition is an important property with respect to the ease of handling (e.g., pumping) of the composition and with respect to the ability of polyurethane-forming mixtures containing the composition to fill molds. It is desirable to minimize viscosity at a given polymer content in order to optimize the ease of handling the composition at a given level of polyurethane load-bearing and modulus enhancement (i.e., at a given polymer content) and in order to facilitate molding such polyurethane-forming mixtures.
In addition to the above-described commercially available polymer/polyol compositions, a wide variety of other polymer/polyol compositions are known in the art. Such compositions are disclosed, for example, in U.S. Pat. Nos. 3,304,273; 3,383,351 and 3,823,201; Canadian Pat. No. 735,010 and German Pat. Nos. 1,152,536 and 1,152,537.
It is an object of this invention to provide improved polymer/polyol compositions.
It is a further object of this invention to provide readily processable polymer/polyol compositions that contain over 20 wt.% of an acrylonitrile-styrene polymer and that can be used to produce polyurethane foams having relatively high load-bearing properties and solid polyurethanes having relatively high modulus.
It is an additional object of this invention to provide stable polymer/polyol compositions that contain relatively low molecular weight polyols.
It is another object of this invention to provide polymer/polyol compositions that have relatively low viscosities at given polymer contents and polyol molecular weights.
Other objects of this invention will be apparent from the description thereof appearing below.